Fabrication method for a multi-layer substrate

ABSTRACT

A method for fabricating a substrate provided with a plurality of layers, includes: providing a steel substrate with an oxide layer including metal oxides on the steel substrate; providing a metal coating layer directly on the oxide layer, the metal coating layer including: at least 8% by weight nickel; at least 10% by weight chromium; and a remainder being iron and impurities from a fabrication process; and providing an anti-corrosion coating layer directly on the metal coating layer.

This is a Divisional of U.S. patent application Ser. No. 15/301,821,filed on Oct. 4, 2016 which is a National Phase of International PatentApplication PCT/IB2014/000485, filed on Apr. 4, 2014. Both abovereferenced applications are hereby incorporated by reference herein.

This invention relates to a multi-layer substrate and a method for thefabrication thereof.

BACKGROUND

Steel sheets are generally covered with a metal coating, the compositionof which varies as a function of the final use of the steel sheet. Thiscoating can, for example, be zinc, aluminum, magnesium or their alloys,can include one or more layers and can be applied using differentcoating technologies known to a person skilled in the art, such as, forexample, vacuum deposition methods, hot-dip coating orelectro-deposition. In the remainder of this description, the term“metal coating” will also be used to designate a coating that includesmetal as well as a coating that includes metal alloy.

The metal coating can first of all be applied by hot-dip coating,whereby this process generally comprises the following steps:

-   -   Annealing of the steel sheet as it passes through a furnace        under an inert or reducing atmosphere to limit the oxidation of        the surface of the sheet;    -   Dip-coating of the sheet as it passes through a bath of metal or        metal alloy in the liquid state so that when it exits the bath,        the sheet is coated with the metal/metal alloy.    -   After the sheet exits the liquid bath, the layer of metal/metal        alloy is dried by spraying a gas on the surface to guarantee a        uniform and regular thickness of this layer.

During the annealing step, before the steel sheet enters the metal bath(in the following portion of the text the terms “metal bath” and “metallayer” are also used to designate any metal alloy bath and thecorresponding metal alloy layers) the sheet is generally heated in adirect flame or radiant tube annealing furnace. However, in spite ofnumerous measures that are taken, such as the control of an inertatmosphere, the use of these furnaces to heat the steel sheet can leadto the formation of metal oxides on the surface, which must then beremoved to ensure the proper wettability of the liquid metal on thesurface of the steel sheet and to prevent the occurrence of uncoatedareas on the surface of the sheet.

This problem is encountered in particular when the composition of thesteel includes significant quantities of easily oxidized elements suchas Si, Mn, Al, Cr, B, P etc. For example, an IF (Interstitial-Free)steel that contains 0.2% by weight Mn, 0.02% by weight Si and 5 ppm B isalready subject to these problems of wettability as a result of thepresence of B which rapidly diffuses to the surface of the sheet andprecipitates the oxides of Mn and Si in the form of continuous films,leading to poor wetting.

More generally, the risk of poor wetting by the liquid metal is alsoencountered in all high-strength steels because they contain at leastone of these easily oxidized elements, such as Dual Phase steels, TRIP(Transformation Induced Plasticity) steels, TWIP (TWinning-InducedPlasticity), electrical steels, etc.

For Dual Phase steels, the quantity of Mn is generally less than 3% byweight, with the addition of Cr, Si or Al in quantities generally lessthan 1% by weight. For TRIP steels, the quantity of Mn is generally lessthan 2% by weight associated with a maximum of 2% by weight of Si or Al.For TWIP steels, the quantity of Mn can be up to 25% by weight, combinedwith Al or Si (maximum 3% by weight).

The metal coating can also be applied by electro-deposition. In thismethod, the steel sheet to be coated is immersed in an electrolyte bathin which one or more soluble anodes are also immersed, the anodesinclude the metal or the metal alloy corresponding to the coating to beapplied to the surface of the sheet. The application of an electriccurrent to the electrolyte bath causes the dissolution of the metal orthe metal alloy of which the anode or anodes are made and the ionsthereby formed are deposited on the surface of the steel sheet to form alayer of metal or metal alloy coating. Prior to entering theelectrolysis bath, the steel sheets must undergo a pickling step toremove the metal oxides that are present on the surface. In fact, forthe electrolysis process to be effective, the medium must necessarily bea conductor, which is not the case if metal oxides are present on thesurface of the steel sheet to be coated. Moreover, the presence of metaloxides can influence the germination and growth of the deposit and thuslead to problems of adherence and quality of the coating(microstructure, density etc.).

The metal coating can also be applied by vacuum deposition. The vacuumdeposition techniques principally require three components:

-   -   A source, which constitutes or contains the material to be        deposited. This source can be, for example, the crucible of a        vacuum evaporator or a sputtering target. The material to be        deposited must leave this source in the form of ions, atoms or        groups of atoms or groups of molecules;    -   A substrate, which corresponds to the part to be coated. The        material originating from the source is affixed to the substrate        to form germs (nucleation), which gradually develop (growth) and        result in a more or less ordered coating layer;    -   A medium, which separates the source from the substrate and        which is the location of the phenomenon of transfer of material        in the vapor phase.

A distinction is made among different types of vacuum deposits as afunction of, among other things, the means used to form the vapor phase.If the vapor phase results from a chemical reaction or the decompositionof a molecule, the process is called CVD, or chemical vapor deposition.On the other hand, if this vapor is produced by a purely physicalphenomenon such as thermal evaporation or ion sputtering, the process isa physical vapor deposition or PVD. PVD deposition processes includesputtering, ion implantation and vacuum evaporation. However, regardlessof the vacuum deposition technique used, it requires a preparation ofthe surface so that the surface of the steel sheet to be coated is freeof metal oxides to guarantee the proper adherence of the metal coatingand to thereby prevent problems of delamination of the coating.

Regardless of the coating method used, the surface condition of thesteel strip before coating is an important factor in the quality of thefinal coating. The presence of metal oxides on the surface of the steelsheet to be coated prevents the proper adherence of the coating to beapplied and can result in zones in which there is no coating on thefinal product or problems related to the delamination of the coating.These metal oxides can be present in the form of a continuous film onthe surface of the steel sheet or in the form of discontinuous points.The metal oxides can also be formed during different steps of theprocess and their composition varies as a function of the grade of steelof which the sheet in question is made. Oxides of this type include, forexample, the iron oxides FeO, Fe₂O₃, aluminum oxide Al₂O₃ as well asMnSiO_(x) or AlSiO_(x).

The removal of these metal oxides requires the execution of anadditional process step, i.e. pickling. In the remainder of thisdescription, pickling means any method that results in the removal ofthe metal oxides formed by oxidation of the underlying metal layer sothat this metal layer appears on the surface, in comparison with, forexample, a brightening method which, although it is a process thatremoves metal oxides, is intended only to remove the surface layer ofmetal oxides without exposing the underlying metal layer.

This removal of metal oxides can be accomplished, for example, by vacuumpickling by magnetron pulverization, which is also called etching. Thisprocess includes creating a plasma between the strip and an auxiliaryelectrode in a gas that makes it possible to generate radicals and/orions. Under normal operating conditions, these ions are acceleratedtoward the surface of the strip to be pickled and blast away surfaceatoms, thereby eliminating the metal oxides present on the surface. Thismethod depends to a great extent on the thickness of the layer of metaloxides to be removed and, depending on the composition of these metaloxides, can generate electric arcs. The process is therefore unstableand not very robust. In addition, it sets a severe limitation on thespeed of the line to obtain a good result, which poses productivityproblems.

It is also possible to pickle the strip by passing it through one ormore successive baths of strong acids such as hydrochloric acid orsulfuric acid, selected as a function of the nature of the metal oxideson the surface and held at a temperature of approximately 80-90° C. Thisprocess generates large quantities of effluents which require subsequenttreatment and is not environmentally friendly.

In addition, this type of pickling poses the problem of controlling thethickness of metal oxides removed to guarantee the proper adherence ofthe subsequent coating.

Finally, it is possible to remove all or part of the layers of metaloxides by mechanical action, for example by using a shot-blastingprocess in which the metal oxides are removed, for example, as a resultof the multiple impacts of small abrasive particles projected withsufficient kinetic energy. However, this type of process directlyimpacts the surface of the strip and is also complicated to implement.Moreover, these processes require working in specific conditions, suchas an inert or reducing atmosphere, for example, to prevent there-oxidation of the metal surfaces by contact with air.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a surfacetreatment method that makes it possible to, among other things, improvethe adherence of a subsequent coating on the substrate and one does notrequire a step to eliminate the oxides present on the surface.

For this purpose, the present invention provides a substrate including aplurality of layers, at least one of which includes metal oxides and isdirectly topped by a layer of metal coating that contains at least 8% byweight nickel and at least 10% by weight chromium, the rest being iron,additional elements and impurities resulting from the fabricationprocess, this metal coating layer being itself directly topped by ananti-corrosion coating layer.

This substrate provided with a plurality of layers can also have thefollowing characteristics, considered individually or in combination:

the substrate further comprising a metal sheet, at least one of thesurfaces of which has a the first layer of oxides, this first layer ofoxides being directly topped by the first layer of metal coating thatcontains at least 8% by weight nickel and at least 10% by weightchromium, the remainder being iron, additional elements and impuritiesresulting from the fabrication process, this first metal coating layerbeing directly topped by the first layer of anti-corrosion coating, thefirst anti-corrosion coating layer being topped by a second layer ofoxides directly topped by a second metal coating layer that contains atleast 8% by weight nickel and at least 10% by weight chromium, theremainder being iron, additional elements and impurities resulting fromthe fabrication process, this second metal coating layer being directlytopped by a second anti-corrosion coating layer;

the metal coating layer, or layers, consists or consist of stainlesssteel containing between 10 and 13% by weight nickel, between 16 and 18%by weight chromium, the remainder being iron and potential impuritiesresulting from the fabrication process;

the metal coating layer, or layers, consists or consist of a layer orlayers of stainless steel containing 0.02% by weight carbon, between 16and 18% by weight chromium, between 10.5 and 13% by weight nickel,between 2 and 2.5% by weight molybdenum, between 0.9 and 1.3% by weightsilicon, between 1.8 and 2.2% by weight manganese, the remainder beingiron and potential impurities resulting from the fabrication process;

the metal coating layer(s) has/have a thickness between 2 and 15 nm;

the anti-corrosion coating layer, or layers, consists or consist, of ametal selected from among the group comprising zinc, aluminum, copper,magnesium, titanium, nickel, chromium, manganese and their alloys;

the anti-corrosion coating layer, or layers, consists or consist of zincor a zinc alloy;

the anti-corrosion coating layer, or layers, consists or consist of aplurality of sub-layers of metal coatings;

at least one anti-corrosion layer is located under the layer of oxidesand is in direct contact with the layer of oxides;

the substrate further comprising a steel sheet located under the layerof oxides; and/or the steel sheet is a steel that has a strength greaterthan or equal to 450 MPa.

The present invention provides a method for the fabrication of asubstrate provided with a plurality of layers in which the metal coatinglayer(s) is/are deposited by a process selected from a vacuum depositionprocess and an electro-deposition process.

This fabrication method may include a deposition process that is amagnetron cathode pulverization process.

The fabrication method may further include depositing the anti-corrosionlayer(s) by a process selected from a vacuum deposition process and anelectro-deposition process.

The present invention further provides method for the preparation of thesurface of a substrate. The method includes at least one layer of metaloxides in which a metal coating containing at least 8% by weight nickeland at least 10% by weight chromium, the rest being iron and theimpurities resulting from the fabrication method, is deposited on saidlayer of oxides without prior pickling of the layer of oxides.

This surface preparation method may further include depositing ananti-corrosion coating on the metal coating.

Other characteristics and advantages of the invention are explained ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the invention, tests have been performed and will bedescribed in the form of non-limiting examples, in particular withreference to the accompanying figures, in which:

FIG. 1 is a schematic illustration of a substrate in a first embodimentof the invention.

FIG. 2 is a schematic illustration of the substrate in a secondembodiment of the invention.

FIG. 3 is a schematic illustration of a substrate in a third embodimentof the invention.

DETAILED DESCRIPTION

FIGS. 1 to 3 illustrate different embodiments of the invention. Thethickness of the layers represented is exclusively for purposes ofillustration and cannot be considered to be a representation of thedifferent layers to scale.

For all of the FIGS. 1 to 3, the term “steel” as used here includes allknown grades of steel and can be, for example, one of the followinggrades of THR (Very High Strength, generally between 450 and 900 MPa) orUHR (Ultra High Strength, generally greater than 900 MPa), steel whichcontain large quantities of oxidizable elements:

-   -   Steels without interstitial elements (IF—Interstitial Free),        which can contain up to 0.1% by weight Ti;    -   Dual-phase steels such as DP 500 steels up to DP 1200 steels        which can contain up to 3% by weight Mn in association with up        to 1% by weight Si, Cr and/or Al,    -   TRIP (TRansformation Induced Plasticity) steels such as TRIP        780, which contains, for example, approximately 1.6% by weight        Mn and 1.5% by weight Si;    -   TRIP or dual-phase steels containing phosphorus;    -   TWIP (TWinning-Induced Plasticity) steels—steels that have a        high content of Mn (generally 17-25% by weight),    -   Low-density steels such as the Fe—Al steels which can contain,        for example, up to 10% by weight Al;    -   Stainless steels, which have a high content of chromium        (generally 13-35% by weight), in association with other alloy        elements (Si, Mn, Al etc.).

FIG. 1 illustrates a first embodiment of a substrate provided withseveral layers in accordance with the present invention. This substrateincludes a steel sheet 1 that has a layer of oxides 2 on at least one ofits surfaces. This layer 2 can be continuous or discontinuous on thesteel surface 1 in question and includes metal oxides from the groupthat includes the iron oxides, chromium oxides, manganese oxides,aluminum oxides, silicon oxides or one or more mixed oxides containingsteel alloy elements such as mixed Mn—Si or Al—Si oxides. The thicknessof this layer of metal oxides 2 can vary, in general, from 3 toapproximately 60 nanometers, for example, and preferably from 3 toapproximately 20 nm.

This oxide layer 2 is therefore not removed by pickling and is coveredwith a layer of a metal coating 3 that contains at least 8% by weightnickel and at least 10% by weight chromium, the remainder includingiron, additional elements such as carbon, molybdenum, silicon,manganese, phosphorus or sulfur and the impurities resulting from thefabrication process. This coating 3 can be, for example, stainlesssteel, and preferably 316 stainless steel (16-18% by weight Cr, 10-14%by weight Ni) its thickness can be, for example, greater than or equalto 2 nm. This metal coating 3 can be applied by any known coatingmethod, and in particular, for example, by magnetron cathodicpulverization or by electro-deposition.

The method for the formation of a coating on a substrate by magnetroncathodic pulverization, which is generally called “sputtering”, iscarried out in a closed enclosure in which a vacuum has been establishedand in which are installed a target and a substrate located opposite thetarget at a certain distance from the latter. The target has a surfacelayer which is oriented toward the face of the substrate on which acoating is to be formed. This surface layer contains at last one of theelements of which the coating to be deposited on the substrate bysputtering is constituted.

The enclosure contains a plasma of an inert gas such as argon.

In one sputtering method, atoms are ejected from the surface of thesurface layer and are deposited in the form of a coating on thesubstrate. A negative voltage is applied to the target and consequentlyto the material of the surface layer to be ejected. As a result, adischarge is generated which creates the plasma formed by ions,electrons and inert gas particles. Positively charged ions areaccelerated toward the target, which is at a negative potential, so thatthey reach the target with sufficient energy to cause the ejection ofatoms from the surface layer. These detached atoms move toward thesubstrate and are deposited on the substrate in the form of areproducible and essentially uniform coating which adheres well to theface of the substrate.

In this first embodiment, the layer 3 of Fe—Ni—Cr metal coating iscovered with a layer of anticorrosion metal coating 4. Thisanticorrosion metal coating layer 4 can include, for example, pure zinc(including the potential impurities resulting from the fabricationprocess), or zinc alloys such as Zn—Al, Zn—Al—Mg, Zn—Mg, Zn—Fe or Zn—Ni.It can also include aluminum, copper, magnesium, titanium, nickel,chromium, pure manganese (including the potential impurities resultingfrom the fabrication method), or their alloys, such as Al—Si or Mg—Al,for example. This anti-corrosion metal coating 4 can be applied by anyknown coating method such as, for example, a sonic vapor jet depositionprocess, which is also called JVD (Jet Vapor Deposition), an electrongun deposition method or plasma-assisted evaporation, which is alsocalled SIP (Self-Induced Plating) and is described in particular inpatent EP0780486.

The JVD method is a vacuum deposition method in which metal vapor isgenerated by inductively heating a crucible containing a bath of thecoating metal in a vacuum enclosure. The steam escapes from the cruciblevia a conduit that transports it to an exit orifice, which is preferablycalibrated, to form a jet at the speed of sound directed at the surfaceof the substrate to be coated.

FIG. 2 illustrates a second embodiment of the present invention. In thisembodiment, the substrate includes as in FIG. 1 a steel sheet 21. Thissteel sheet 21 is coated with a layer of an aluminum-basedanti-corrosion coating 25, such as, for example, an aluminum-siliconcoating (10-12% by weight Si). This aluminum-based coating 25 can bedeposited by hot dipping, and can have a thickness of between 10 and 30μm, for example. This aluminum-based coating layer 25 is topped by alayer of metal oxides 22. This layer 22 can be continuous ordiscontinuous over the surface of the aluminum-based coating 25 inquestion and can include aluminum oxides and/or mixed aluminum oxidessuch as Al—Si oxides. The thickness of this layer of metal oxides 22 canin general vary from 3 to approximately 60 nanometers, preferably from 3to approximately 20 nm.

This layer of oxides 22 is therefore not removed by pickling and iscovered by a layer of a metal coating 23 that contains at least 8% byweight nickel and at least 10% by weight chromium, with the remainderincluding iron, additional elements as disclosed above and theimpurities resulting from the fabrication process. This metal coating 23can be stainless steel, for example, and preferably stainless steel 316(16-18% by weight Cr, 10-14% weight Ni). This metal coating 23 can beapplied by any known coating method and can have a thickness, forexample, greater than or equal to 2 nm.

This layer of metal coating 23 in this second embodiment is topped by alayer of anti-corrosion metal coating 24 selected from among theanti-corrosion metal coatings described with reference to the firstembodiment. This anti-corrosion metal coating 24 can be applied by anyknown coating process, such as, for example, a vacuum method or a hotdip method, optionally followed by a post-diffusion treatment.

Coatings that can be considered, for example, include a layer of steel21 coated by an Al—Si-base coating 25, whereby this coating 25 is toppedby a layer of oxides 22 composed of mixed Al—Si oxides, the oxides layer22 being coated by a layer 23 of stainless steel 316, this layer 23 ofstainless steel being coated with a Zn—Mg alloy anti-corrosion coating24.

FIG. 3 illustrates a third embodiment of the present invention. In thisthird embodiment, the substrate includes, as in the first embodiment, asteel sheet 31 with a first layer of oxides 32 on at least one of itssurfaces. This first layer 32 can be continuous or discontinuous overthe surface of the steel 31 and contain metal oxides from the groupcomprising of, for example, the iron oxides, chromium oxides, manganeseoxides, aluminum oxides, silicon oxides or one of the mixed oxidescontaining the alloy elements of the steel such as mixed Al—Si or Mn—Sioxides. The thickness of this first layer of metal oxides 32 can vary,in general, from 3 to approximately 60 nm, for example, and preferablyfrom 3 to approximately 20 nm.

As in the first embodiment, this layer of oxides 32 is therefore notremoved by pickling and is covered by a layer of a metal coating 33 thatcontains at least 8% by weight nickel and at least 10% by weightchromium, whereby the remainder includes iron, additional elements asdisclosed above and the impurities resulting from the fabricationprocess. This coating 33 can be, for example, stainless steel, andpreferably stainless 316 (16-18% by weight Cr, 10-14% by weight Ni). Thethickness of this layer of metal coating 33 can, for example, be greaterthan or equal to 2 nm. This metal coating 33 can be applied by any knowncoating process, and in particular, for example, by magnetron cathodicpulverization or by electro-deposition. In this embodiment, the layer 33of Fe—Ni—Cr metal coating is covered by a first layer of anti-corrosionmetal coating 34. This first layer of anti-corrosion metal coating 34can include, for example, pure zinc (containing the potential impuritiesresulting from the fabrication process), or zinc alloys such as Zn—Al,Zn—Al—Mg, Zn—Mg or Zn—Ni. It can also include aluminum, copper,magnesium, titanium, nickel, chromium, pure manganese (containing thepotential impurities resulting from the fabrication process) or theiralloys, such as, for example, Al—Si or Mg—Al. This first layer ofanti-corrosion metal coating 34 can be applied by any known coatingmethod, such as, for example, a process carried out in a vacuum or ahot-dip process.

In this third embodiment, the first layer of anti-corrosion metalcoating 34 is topped by a second layer of metal oxides 36. This layer 36can be continuous or discontinuous on the surface of the anti-corrosionmetallic coating 34 and can include oxides, the composition of whichdepends on the constituent material of the anti-corrosion metal coating34. For example, these oxides can be zinc oxides, aluminum oxides ormixed Al—Si, Zn—Mg or Zn—Al oxides. The thickness of this layer of metaloxides 36 can vary, in general, from 3 to approximately 60 nm, forexample, and preferably from 3 to approximately 20 nm.

This second layer of oxides 36 is not eliminated by pickling and iscovered by a layer of a metal coating 37 that contains at least 8% byweight nickel and at least 10% by weight chromium, with the remainderbeing iron, additional elements as disclosed above and the impuritiesresulting from the fabrication process. This coating 37 can, forexample, be stainless steel, and preferably stainless steel 316 (16-18%by weight Cr, 10-14% by weight Ni). This metal coating 37 can be appliedby any known coating process and can but need not be identical to themetal coating 33. The thickness of this layer of metal coating 37 can,for example, be greater than or equal to 2 nm.

In this third embodiment, this layer of metal coating 37 is topped by asecond layer of anti-corrosion metal coating 38 selected from among theanti-corrosion metal coatings described with reference to the firstembodiment. This anti-corrosion metal coating 38 can be applied by anyknown coating method, such as for example a vacuum method or a hot-dipmethod, optionally followed by a post-diffusion treatment. Thisanti-corrosion metal coating 38 can but need not be identical to thefirst anti-corrosion metal coating 34.

For example, consideration can be given to a layer of steel 31, a firstlayer of iron oxides 32, a first metal coating 33 consisting ofstainless steel 316, a first anti-corrosion metal coating 34 consistingof an Al—Si alloy, a second layer of oxides 36 consisting of mixed Al—Sioxides, a second metal coating 37 consisting of stainless steel 316 andthe second anti-corrosion metal coating 38 consisting of a Zn—Al—Mgalloy.

The present invention will now be explained on the basis of testsperformed for purposes of illustration only and not intended to belimiting.

Tests

Acceptance Criteria

T-Bend Test

The purpose of this test is to determine the adherence of the coatingsby bending the coated sheet at an angle of 180°. The bending radiusapplied is equal to twice the thickness of the substrate used (whichcorresponds to a “2T” bend). The adherence of the coating is verified bythe application of an adhesive tape. The result of the test is judgedpositive if the coating remains on the tested sheet and does not appearon the adhesive tape after the tape is removed.

The adhesive tape used for the performance of this test in the testsdescribed below is a commercial adhesive, TESA4104.

Cup Test

This method consists of performing a stamping test during which a cup isformed. This deformation of the material as well as of the metal coatingidentifies potential problems relating to the adherence of the metaldeposit on the substrate. The loss of adherence (or dusting) isexpressed in a reduction of the weight of the cup, which is weighedbefore and after stamping, in g/m².

Daimler Bending

The first stage of this test consists of applying a punch to the coatedsteel sheet and measuring the bending angle at which a reduction instrength greater than or equal to 30 kN is observed. This drop instrength corresponds to the cracking of the substrate. The adhesion testof the metal coating then consists of bending the coated sheet at anangle close to but less than this cracking point and checking theadherence of the zinc by the application of an adhesive coating. Thetest result is judged positive if the zinc coating remains on the sheetand does not appear on the adhesive tape after the tape is removed.

The adhesive tape used to perform the tests described below has anadhesive strength between 400 and 460 N/m, e.g. Scotch® 3M595.

Tests—1—Adhesion

For all of the tests the composition of the stainless steel 316L used is0.02% C, 16-18% Cr, 10.5-13% Ni, 2-2.5% Mo, 1% Si, 2% Mn, 0.04% P, 0.03%S. The percentages are percentages by weight, with the remainder beingiron and potential impurities resulting from fabrication.

A series of 8 specimens of DP1180 steel sheet of the type sold byArcelorMittal was prepared. The exact composition of the steel used forthe samples is 0.15% C, 1.9% Mn, 0.2% Si, 0.2% Cr, and 0.013% Ti. Thepercentages are percentages by weight, with the remainder being iron andpotential impurities resulting from fabrication.

All of the samples were subjected to the steps described below:

-   -   Brightening of the steel sheet by passing it through a bath        containing formic acid HCOOH or sulfuric acid H₂SO₄ held at a        temperature below 50° C. The purpose of this step is to remove        the upper layer of iron oxides of type FeO, but it does not        remove the underlying layer of oxides.    -   Rinsing with water.    -   Drying to remove the water adsorbed during the rinsing step.    -   Insertion of the strip into a vacuum chamber having a pressure        P<10⁻³ mbar.    -   Vacuum evaporation deposition of a layer of 5 μm of zinc.

Specimens 2 and 6 which are of the type described by the prior art aresubjected after this drying step to an etching step to remove the metaloxides that are present on the surface of the steel sheet.

Specimens 1, 5 and 9 in accordance with preferred embodiments of thepresent invention are then subjected after the step of insertion intothe vacuum chamber to a step in which they are coated with a layer of 10nm of stainless steel 316L by magnetron cathodic pulverization (seedescription of this method above).

Specimens 4 and 8 are subjected after the insertion into the vacuumchamber to a step in which they are coated with a layer of 10 nm oftitanium by magnetron cathodic pulverization (see description of thismethod above).

Specimen 9 was not subjected to the brightening step.

The characteristics of each specimen are presented in the table below:

Specimen number Brightening Etching Coating 1* H2SO4 No Stainless 316 2H2SO4 Yes No 3 H2SO4 No No 4 H2SO4 No Ti 5* HCOOH No Stainless 316 6HCOOH Yes No 7 HCOOH No No 8 HCOOH No Ti 9* None No Stainless 316*Specimen according to the present invention

All of these specimens were then subjected to the T-bend and cup testsdescribed above.

The results of the “Cup test” are expressed as a percentage of loss ofzinc compared to the initial weight of zinc of the cup.

The results are presented in the table below.

Cup test Specimen number T-bend % loss Conclusion 1* OK 4.5 OK 2 OK 8.4OK 3 NOK 79.8 NOK 4 OK 42 NOK 5* OK 5.9 OK 6 OK 3.3 OK 7 NOK 67 NOK 8 OK29 NOK 9* OK 10.5 OK

Specimens 2 and 6 as described by the prior art had positive results forboth tests. This result is not surprising because these two specimens ofthe prior art were subjected to an etching step which makes it possibleto remove the metal oxides present on the surface and thereforeguarantees a good surface condition before coating to obtain a properadherence of the zinc coating.

For the specimens 1, 5 and 9 according to the present invention, the twotests are conclusive and indicated a good adherence of the zinc,equivalent to that which could be obtained with an etching step,regardless of the acid used for the brightening and even without a priorbrightening step (specimen 9).

In addition, specimens 4 and 8 which had a titanium coating instead ofthe stainless steel 316 coating did not provide any conclusive resultsin the two tests performed because the adherence of the zinc coating wasinsufficient.

Tests—2

A series of 12 specimens was prepared with different grades of steel anddifferent process parameters. The set of specimens was manufacturedaccording to the invention and was subjected to the following processsteps:

-   -   Alkaline degreasing to eliminate potential organic residues        present on the surface of the steel sheet. This degreasing was        performed by dipping the strip in a bath of a basic solution        held at 60° C. The dip time as well as the characteristics of        the bath used for each specimen are indicated in the table        below.    -   Rinsing with water.    -   Drying to eliminate the water adsorbed during the rinsing step.    -   Insertion of the strip into a vacuum chamber which is at a        pressure P<10⁻³ mbar.    -   Preheating of the strip to a temperature of approximately 120°        C.    -   Depositing of a layer of stainless steel 316L by magnetron        cathodic pulverization (see description of this method above).        The thickness of this layer of stainless steel 316L varies from        one specimen to another and is indicated in the table below.    -   Deposition of a layer of zinc by JVD (See description of this        process above).

The characteristics of each specimen are listed in the table below:

Thickness Thick- Sheet of ness thick- Type of stainless of Zn No. Steel(mm) oxides Degreasing steel (nm) (μm) 10 DP1180 1.22 mm ChromiumNovaclean ™ 2.5 nm   8 μm 11 oxides and 300M 2% +   5 nm 12 iron oxidesRidosol ®  10 nm 13 MS1500  1.1 mm Iron oxides 0.2% 2.5 nm   8 μm 14 60°C.-10   5 nm 15 sec  10 nm 16 Trip  0.8 m  Mixed Mn- pH = 12 2.5 nm   8μm 17 Dual Si   5 nm 18 1200 oxides  10 nm 19 Usibor ® 1.5 mm MixedS5183   3 nm 4.5 μm 20 AS150 Al-Si 60° C.-15  15 nm oxides sec pH = 14

Novaclean™ and Ridosol® are products sold by Henkel. Gardoclean S5183 issold by Chemetall.

Specimens 10 to 12 were prepared starting with DP1180 steel sheets assold by ArcelorMittal. The exact composition of the steel used for thespecimens was 0.15% C, 1.9% Mn, 0.2% Si, 0.2% Cr, and 0.013% Ti. Thepercentages are percentages by weight, the remainder being iron andpotential impurities resulting from fabrication. The majority of themetal oxides present on the surface of the steel sheet are chromiumoxides and iron oxides. The oxidized steel sheet was coated with a layerof stainless steel 316L, the thickness of which varied from one specimento another, and then a layer of zinc with a thickness between 7.5 and 8μm.

The specimens 13 to 15 were prepared starting with MS1500 steel sheetsas sold by ArcelorMittal. MS stands for martensitic steel. The exactcomposition of the steel used for the specimens is 0.225% C, 1.75% Mn,0.25% Si, 0.2% Cr, 0.035% Ti. The percentages are percentages by weight,the remainder being iron and potential impurities resulting fromfabrication. The majority of the metal oxides present on the surface ofthe steel sheet are iron oxides. The oxidized steel sheet was coatedwith a layer of stainless steel 316L, the thickness of which varied fromone specimen to another, and then a layer of zinc with a thicknessbetween 7.5 and 8 μm.

Specimens 16 to 18 were prepared starting with Trip Dual 1200 steelsheets as sold by ArcelorMittal. The exact composition of the steel usedfor the specimens is 0.2% C, 2.2% Mn, 1.5% Si, and 0.2% Cr. Thepercentages are percentages by weight, the remainder being iron andpotential impurities resulting from fabrication. The majority of themetal oxides present on the surface of the steel sheet are mixedmanganese and silicon oxides. The oxidized steel sheet was coated with alayer of 316L stainless steel, the thickness of which varied from onespecimen to another, followed by a layer of zinc with a thicknessbetween 7.5 and 8 μm.

Specimens 19 and 20 were prepared starting with Usibor® AS150 steelsheets. The steel in question is a Usibor® steel coated with a layer of150 g/m² of AluSi@, an aluminum- and silicon-based coating. The exactcomposition of the AluSi@ coating used for these specimens was 90% Al,10% Si. The percentages are expressed by weight. The majority of themetal oxides present on the surface of the steel sheet are mixedaluminum and silicon oxides. The oxidized steel sheet was covered with alayer of stainless steel 316L, the thickness of which varied from onespecimen to another, followed by a layer of zinc in a thickness between4 and 5 μm.

This set of specimens was then subjected to the T-bend and DaimlerBending tests as described above.

The results are presented in the table below:

Daimler Bending No. T-Bend Angle Result 10 OK 108° OK 11 OK 108° OK 12OK 108° OK 13 OK 137° OK 14 OK 137° OK 15 OK 137° OK 16 OK  89° OK 17 OK 89° OK 18 OK  89° OK 19 OK Not tested 20 OK Not tested

These results prove that with the substrate in accordance with apreferred embodiment of the present invention, the zinc coating isadherent regardless of the composition of the metal oxides present onthe surface or of the pH of the solution used for degreasing. Inaddition, the results of the adhesion tests of the zinc coating arepositive beginning with the application of a thickness of 2.5 nm ofstainless steel 316.

Test—3

A series of 2 specimens was prepared starting with Usibor® steel. The 2specimens were subjected to the following process steps:

-   -   Alkaline degreasing to remove any potential organic residue that        may be present on the surface of the steel sheet. This        degreasing is performed by dipping the strip in a bath of a        basic solution held at 60° C. The dip time as well as the        characteristics of the bath used for each specimen are indicated        in the table below.    -   Rinsing with water.    -   Drying to remove the water adsorbed during the rinsing step.    -   Insertion of the strip into a vacuum chamber which is at a        pressure of P<10⁻³ mbar.    -   Deposition of a metal coating.

Specimen 31 as described by the prior art is subjected after the dryingstep to an etching step to remove the metal oxides present on thesurface of the steel sheet.

Specimen 32 as claimed by the invention is then subjected after the stepof the insertion into a vacuum chamber to a step in which it is coatedwith a layer of stainless steel 316L by magnetron cathodic pulverization(see description of this process above).

The thickness of this coating is 10 nm.

Following the etching step or following the step of the deposition of alayer of stainless steel 316L, the specimens were coated with a layer of5 μm of aluminum by magnetron cathodic pulverization.

The characteristics of each specimen are presented in the table below:

Coating stainless Metal Number Steel sheet Etching steel 316 coating 31Usibor ® Yes No 5 μm Al 32* Usibor ® No 10 nm 5 μm Al *Specimen asclaimed by the invention.* Specimen as claimed by the invention.

The adhesion of the top metal coating of each specimen was then testedby means of an adhesive tape applied to the flat specimen and thenremoved. The adhesive tape used has an adhesive strength between 400 and460 N/m, e.g. Scotch® 3M595.

The result is positive if the coating remains on the surface of thespecimen and does not appear on the adhesive tape when the tape isremoved. For all of the specimens tested, the adhesive tape did notcontain any coating after the test, which means that the coating isadherent. This result was expected for specimen 31 of the prior artbecause it had been subjected to an etching step which removed the metaloxides that were present on the surface of the steel sheet, whether ornot it was coated. On the other hand, these results show that this stepof removing the oxides can be eliminated by the deposition of a layer ofstainless steel 316L directly on the oxidized surface, because theresults of the adhesion test are also positive with the configuration ofa preferred embodiment of the present invention.

What is claimed is:
 1. A method for fabricating a substrate providedwith a plurality of layers, the method comprising: providing a steelsubstrate with an oxide layer including metal oxides on the steelsubstrate; providing a metal coating layer directly on the oxide layer,the metal coating layer including: at least 8% by weight nickel; atleast 10% by weight chromium; and a remainder being iron and impuritiesfrom a fabrication process; and providing an anti-corrosion coatinglayer directly on the metal coating layer; wherein the providing of theanti-corrosion layer includes depositing the anti-corrosion layer by anelectro-deposition process.
 2. The method as recited in claim 1 whereinthe providing of the metal coating layer includes depositing the metalcoating layer by a vacuum deposition process.
 3. The method as recitedin claim 1 wherein the providing of the metal coating layer includesdepositing the metal coating layer by an electro-deposition process. 4.The method as recited in claim 1 wherein the providing of the metalcoating layer occurs includes a magnetron cathode pulverization process.5. The method as recited in claim 1 wherein the steel substrate with theoxide layer is provided without pickling the oxide layer.
 6. The methodas recited in claim 1 wherein the oxide layer is in direct contact withthe steel substrate.
 7. A method for fabricating a substrate providedwith a plurality of layers, the method comprising: providing a steelsubstrate depositing an aluminum-based coating on the steel substrate,an oxide layer being directly on the aluminum-based coating, the oxidelayer including metal oxides; providing a metal coating layer directlyon the oxide layer, the metal coating layer including: at least 8% byweight nickel; at least 10% by weight chromium; and a remainder beingiron and impurities from a fabrication process; and providing ananti-corrosion coating layer directly on the metal coating layer.
 8. Themethod as recited in claim 7 wherein the aluminum-based coating isdeposited by hot dipping.
 9. The method as recited in claim 7 whereinthe aluminum-based coating has a thickness of between 10 and 30 μm. 10.The method as recited in claim 7, wherein the providing of theanti-corrosion layer includes depositing the anti-corrosion layer by anelectro-deposition process.
 11. The method as recited in claim 7 whereinthe providing of the metal coating layer includes depositing the metalcoating layer by a vacuum deposition process.
 12. The method as recitedin claim 7 wherein the providing of the metal coating layer includesdepositing the metal coating layer by an electro-deposition process. 13.The method as recited in claim 7 wherein the providing of the metalcoating layer includes a magnetron cathode pulverization process.
 14. Amethod for fabricating a substrate provided with a plurality of layers,the method comprising: providing a steel substrate with an oxide layerincluding metal oxides on the steel substrate; providing a metal coatinglayer directly on the oxide layer, the metal coating layer including: atleast 8% by weight nickel; at least 10% by weight chromium; and aremainder being iron and impurities from a fabrication process; andproviding an anti-corrosion coating layer directly on the metal coatinglayer; and providing a further metal oxide layer directly on theanti-corrosion coating layer, a further metal coating layer directly onthe further metal oxide layer; and a further anti-corrosion coatinglayer directly on the further metal coating layer.
 15. The methodaccording to claim 14, wherein the further metal coating layer includesat least 8% by weight nickel; at least 10% by weight chromium; and aremainder being iron and impurities from a fabrication process.
 16. Themethod as recited in claim 14, wherein the providing of theanti-corrosion layer includes depositing the anti-corrosion layer by anelectro-deposition process.
 17. The method as recited in claim 14wherein the providing of the metal coating layer includes depositing themetal coating layer by an electro-deposition process.
 18. A method forfabricating a substrate provided with a plurality of layers, the methodcomprising: providing a steel substrate with an oxide layer includingmetal oxides on the steel substrate; providing a metal coating layerdirectly on the oxide layer, the metal coating layer including: at least8% by weight nickel; at least 10% by weight chromium; and a remainderbeing iron and impurities from a fabrication process; and providing ananti-corrosion coating layer directly on the metal coating layer;wherein the providing of the metal coating layer includes depositing themetal coating layer by an electro-deposition process.
 19. The method asrecited in claim 18 wherein the providing of the anti-corrosion layerincludes depositing the anti-corrosion layer by a vacuum depositionprocess.
 20. The method as recited in claim 18 wherein the steelsubstrate with the oxide layer is provided without pickling the oxidelayer.
 21. The method as recited in claim 18 wherein the oxide layer isin direct contact with the steel substrate.